SACRAMENTO, Calif. (KXTV) - Report cards have long been a source of stress for students and their families, but a fitness report card is raising more concerns for some parents.

The so-called "fat letters," which tell parents their children's body mass index doesn't make the grade, are on the rise across the country.

Body Mass Index (BMI) is a measurement that uses a person's weight and height to gauge body fat. It's a tool included in an array of tests to measure physical fitness, but some worry that taken out of context, it could do more harm than good.

School weigh-ins followed by report cards sent home telling how students are tipping the scales are causing some parents to worry about the reliance on BMI as a measurement of their children's health. "I've noticed that people put a lot of emphasis on a number when actually I think they should be putting more emphasis on their actual fitness," Sacramento parent Lana Rossi said. "If they're able to run and play, and do all that stuff, for an extended period of time, to me they're fit."

"I wouldn't want to be told what my BMI is, so I can imagine an adolescent girl that's growing probably wouldn't want to know either," Sandra Bacchi added as she picked up her grandson from school.

In California, BMI remains part of the Physical Fitness Test given to students in 5th, 7th and 9th grades. It's a tool supported by some pediatricians.

"Right now, it's the best measurement that we have to determine whether a child's weight is healthy or unhealthy," Pediatrician Lanre Omojokun Falusi said.

But many therapists disagree. Jennifer Lombardi, Executive Director of Sacramento's Summit Eating Disorders and Outreach Program, said BMI is so ineffective, clinicians at her program don't even use it, and the potential for emotional harm to a child is even more significant.

"I have heard countless stories in schools where the scales are brought into the schools, and children are weighed in front of each other at young ages and not given any context whatsoever to put that number in," Lombardi said.

Lombardi said there needs to be a thorough approach to educating children and their families about developmental norms for weight and how to lead healthy lifestyles. She also questions whether BMI should be a part of fitness testing at all.

"I absolutely think that the methodology needs to be reviewed very carefully," Lombardi said. "I completely understand that the intention behind it is good, but again the approach is really the issue."

BMI has been part of the California Department of Education's fitness testing since 1987. Schools also use skin fold measurements and a bioelectric analysis to assess body composition.